Resistance variable element methods and apparatuses

ABSTRACT

Apparatus and methods are disclosed, including a method that performs a first operation on a first resistance variable element using a common source voltage, a first data line voltage and a first control gate voltage, and then performs a second operation on a second resistance variable element using the common source voltage, a second data line voltage and a second control gate voltage. Additional apparatus and methods are described.

PRIORITY APPLICATION

This application is a continuation of U.S. application Ser. No.13/947,807, filed Jul. 22, 2013, which is incorporated herein byreference in its entirety.

BACKGROUND

Semiconductor memory devices are used in many electronic devices such aspersonal digital assistants (PDAs), laptop computers, mobile phones anddigital cameras. Some of these semiconductor memory devices have arraysof resistance variable memory cells.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments are illustrated by way of example and not limitation inthe figures of the accompanying drawings in which:

FIG. 1 is an electrical schematic diagram of an apparatus in the form ofa resistance variable memory cell according to various embodiments ofthe invention;

FIG. 2 is an electrical schematic diagram of an apparatus in the form ofa portion of an array of resistance variable memory cells according tovarious embodiments of the invention;

FIG. 3 is a timing diagram for the array of FIG. 2 according to variousembodiments of the invention where each of the resistance variablememory cells may be similar or identical to the resistance variablememory cell shown in FIG. 1;

FIG. 4 is a timing diagram for the array of FIG. 2 according to variousembodiments of the invention where each of the resistance variablememory cells may be similar or identical to the resistance variablememory cell shown in FIG. 1;

FIG. 5 is an electrical schematic diagram of an apparatus in the form ofa resistance variable memory cell according to various embodiments ofthe invention;

FIG. 6 is an electrical schematic diagram of an apparatus in the form ofa resistance variable memory cell according to various embodiments ofthe invention;

FIG. 7 is a timing diagram for the array 200 of FIG. 2 according tovarious embodiments of the invention where each of the resistancevariable memory cells may be similar or identical to the resistancevariable memory cell shown in FIG. 6;

FIG. 8 is a timing diagram for the array of FIG. 2 according to variousembodiments of the invention where each of the resistance variablememory cells may be similar or identical to the resistance variablememory cell shown in FIG. 6;

FIG. 9 is an electrical schematic diagram of an apparatus in the form ofa resistance variable memory cell according to various embodiments ofthe invention;

FIG. 10 is a flow diagram of a method according to various embodimentsof the invention; and

FIG. 11 is a block diagram of an apparatus in the form of a memorydevice according to various embodiments of the invention.

DETAILED DESCRIPTION

For the purposes of this document, an “apparatus” can refer to any of anumber of structures, such as circuitry, a device or a system. In thisdescription, a transistor is described as being switched on to assume anactivated state when it is rendered conductive by a control gatevoltage. The transistor is described as being switched off to assume aninactive state when it is rendered non-conductive by a control gatevoltage. Potentials refer to electrical potentials.

A resistance variable memory cell has an architecture in whichresistance states of a resistance variable element correspond to storeddata. The resistance states can include a low resistance state (LRS) anda high resistance state (HRS). A resistance variable element withmultiple material regions can have more than two resistance states.First data may be written by applying a predetermined drive current to aresistance variable memory cell in a first direction. Writing the firstdata may also be called programming the resistance variable memory cellor setting the resistance variable memory cell, both of which beingreferred to hereinafter as programming the resistance variable memorycells. Second data may be written by applying a predetermined drivecurrent to the resistance variable memory cell in a second directionopposite to the first direction. Writing the second data may also becalled erasing the resistance variable memory cell or resetting theresistance variable memory cell, both of which being referred tohereinafter as erasing the resistance variable memory cell. Resistancevariable memory cells can be arranged in a resistive random accessmemory (RRAM) device.

Resistance variable memory cells can be programmed or erased with asubstantial drive current through an access device. The access devicemay be a field-effect transistor (FET), for example. Many RRAM memoryarray architectures have a common source design in which a potential ofa common source may be substantially constant during both program anderase operations to reduce power dissipation and write delay. Apotential may be substantially constant if it does not change more than0.2 volts in either a positive or a negative direction. The potential ofthe common source can have a minimum limit based on characteristics ofthe access device and a voltage used to program or erase the resistancevariable element. A non-zero potential on the common source can reducecurrent in the access device in an RRAM memory cell. The potential onthe common source can reduce an effective gate-source voltage of theaccess device and increase the threshold voltage of the access devicedue to a reverse bias between source and body terminals of the accessdevice. The substantially constant potential of the common source duringprogram and erase operations can limit the drive current in at least oneof the operations. The challenge noted above, as well as others, can beaddressed by programming or erasing the resistance variable memory cellsin two acts. A control gate voltage of the access device is raised foran erase operation when a data line (e.g., a bit line) is at a higherpotential with respect to the common source. The control gate voltage islowered for a program operation when the data line is at a lowerpotential with respect to the common source.

FIG. 1 is an electrical schematic diagram of an apparatus in the form ofa resistance variable memory cell 100 according to various embodimentsof the invention. The resistance variable memory cell 100 includes aresistance variable element 110 coupled between a data (e.g., bit) line120 and an access device 130. A data line voltage may be provided on thedata line 120 when an operation is performed on the resistance variableelement 110. The access device 130 is coupled between the resistancevariable element 110 and a common source 140 (e.g., a common sourceplate, a common source line, a common source slot or other common sourcestructure). The access device 130 is a FET and in particular ann-channel FET. The access device 130 includes a gate terminal 150coupled to an access (e.g., word) line (not shown), a first terminal 160coupled to the resistance variable element 110 and a second terminal 170coupled to the source 140. The access device 130 can be controlled by acontrol gate voltage on the gate terminal 150 and provided on the accessline. The source 140 may be coupled to thousands or millions of otherresistance variable memory cells and can have a common source voltagethat is substantially constant. The access device 130 may allow currentto flow between the data line 120 and the source 140 when it is switchedon by the potential on its gate terminal 150. The first terminal 160 canbe a drain or a source and the second terminal 170 can be a drain or asource depending on the direction of current in the access device 130.The data line 120 may be used to sense (e.g., read) a data state of theresistance variable element 110. The data state of the resistancevariable element 110 can be read by measuring a resistance value of theresistance variable element 110 which can include sensing a value of acurrent flowing through the resistance variable element 110.

FIG. 2 is an electrical schematic diagram of an apparatus in the form ofa portion of an array 200 of resistance variable memory cells accordingto various embodiments of the invention. The array 200 can be formed ona semiconductor substrate (not shown). The array 200 includes resistancevariable memory cells 201, 202, 203, 211, 212, 213, 221, 222 and 223.Each of the resistance variable memory cells 201-223 may be similar oridentical to the resistance variable memory cell 100 shown in FIG. 1 andincludes the access device 130 coupled to the resistance variableelement 110.

The resistance variable memory cells 201, 211 and 221 are in a first row250 and the access devices 130 of the resistance variable memory cells201, 211 and 221 are coupled to a first access line 252. The resistancevariable memory cells 202, 212 and 222 are in a second row 254 and theaccess devices 130 of the resistance variable memory cells 202, 212 and222 are coupled to a second access line 256. The resistance variablememory cells 203, 213 and 223 are in a third row 258 and the accessdevices 130 of the resistance variable memory cells 203, 213 and 223 arecoupled to a third access line 259.

The resistance variable memory cells 201, 202 and 203 are in a firstcolumn 260 and the resistance variable elements 110 of the resistancevariable memory cells 201, 202 and 203 are coupled to a first data line262. The resistance variable memory cells 211, 212 and 213 are in asecond column 264 and the resistance variable elements 110 of theresistance variable memory cells 211, 212 and 213 are coupled to asecond data line 266. The resistance variable memory cells 221, 222 and223 are in a third column 268 and the resistance variable elements 110of the resistance variable memory cells 221, 222 and 223 are coupled toa third data line 269. The array 200 may have more or less than the nineresistance variable memory cells 201-223 shown in FIG. 2.

With reference to FIG. 1 and FIG. 2, the resistance variable memory cell100 can be programmed to store a first value (e.g., a logic “1”) bydriving a first current through the resistance variable element 110 in afirst direction. The resistance variable memory cell 100 can be erasedto store a second value (e.g., a logic “0”) by driving a second currentthrough the resistance variable element 110 in a second directionopposite to the first direction. The second current may be substantiallyequal to the first current. The access device 130 is biased to conductthe first current in the first direction and the second current in thesecond direction. The gate terminal 150 can be biased by a first controlgate voltage during programming of the first value and by a differentsecond control gate voltage during erasing to the second value toprovide sufficient drive current through the resistance variable element110. Two or more of the resistance variable memory cells 201-223 may beprogrammed or erased at the same time with the same voltage on one ormore of the access lines 252, 256 and 259. The first value is programmedinto one or more of the resistance variable memory cells 100 at a firsttime, and one or more of the resistance variable memory cells 100 iserased to store the second value at a second time.

FIG. 3 is a timing diagram 300 for the array 200 of FIG. 2 according tovarious embodiments of the invention where each of the resistancevariable memory cells 201-223 may be similar or identical to theresistance variable memory cell 100 shown in FIG. 1. The timing diagram300 illustrates voltages in the array 200 during a programming operationand/or an erasing operation for the resistance variable memory cells201, 211 and 221 in the first row 250. The voltages are represented on avertical axis 302 and time t is represented on a horizontal axis 304.Data line voltages on the data lines 120, 262, 266 and 269 areillustrated at the bottom of the timing diagram 300. A control gatevoltage on the access line 252 and the gate terminals 150 of the accessdevices 130 is illustrated above the data line voltages. Control gatevoltages on the access lines 256 and 259 may be the same as the controlgate voltage on the access line 252.

The control gate voltage on the access line 252 is at V_(WL) _(_) _(low)which can be a reference voltage (e.g., ground) before programmingbegins. Programming begins at a time t1 when the control gate voltage onthe access line 252 rises to a first pulse at a voltage V_(WL) _(_)_(highA) which is sufficient to switch on the access device 130 toprogram the first value into one or more of the resistance variablememory cells 201-223. Each pulse comprises a raised (or lowered)electrical potential of a limited duration. One or more of the datalines 262, 266 and 269 are held at a standby data line voltage. Thestandby data line voltage can be substantially equal to a source voltageV_(PL) which is the potential of the source 140 such that none of theresistance variable memory cells 201-223 coupled to a data line 262, 266and 269 at the source voltage V_(PL) is programmed or erased. One ormore of the data lines 262, 266 and 269 are brought to a lower voltageV_(BL) _(_) _(low) at the time t1 to program the resistance variablememory cells 201, 211 and 221 coupled to the data lines 262, 266 and 269at V_(BL) _(_) _(low) to the first value. The voltage V_(BL) _(_) _(low)is lower than the source voltage V_(PL). The pulse on the access line252 ends at a time t2 when the potential of the access line 252 falls toV_(WL) _(_) _(low). The potential of the data lines 262, 266 and 269 (atV_(BL) _(_) _(low)) is raised to the source voltage V_(PL) at the timet2 to end the programming. One or more of the resistance variable memorycells 201, 211 and 221 is programmed to the first value during the pulseon the access line 252 between the times t1 and t2.

Erasing begins at a time t3 when the control gate voltage on the accessline 252 rises from V_(WL) _(_) _(low) to begin a second pulse at avoltage V_(WL) _(_) _(highB) which is sufficient to switch on the accessdevice 130 to erase the second value into one or more of the resistancevariable memory cells 201-223. The voltage V_(WL) _(_) _(highB) ishigher than the voltage V_(WL) _(_) _(highA). A difference between thevoltage V_(WL) _(_) _(highA) and the voltage V_(WL) _(_) _(highB) isless than or equal to the source voltage V_(PL). The voltage V_(WL) _(_)_(highB) may be substantially equal to the voltage V_(WL) _(_) _(highA)plus the source voltage V_(PL). A first voltage may be substantiallyequal to a second voltage if it does not differ from the second voltageby more than 0.2 volts. One or more of the data lines 262, 266 and 269are held at the source voltage V_(PL) such that none of the resistancevariable memory cells 201-223 coupled to a data line 262, 266 and 269 atthe source voltage V_(PL) is erased. One or more of the data lines 262,266 and 269 are raised to a higher voltage V_(BL) _(_) _(high) at thetime t3 to erase one or more of the resistance variable memory cells201, 211 and 221 coupled to the data lines 262, 266 and 269 at V_(BL)_(_) _(high) to the second value. The voltage V_(BL) _(_) _(high) ishigher than the source voltage V_(PL). The pulse on the access line 252ends and the potential of the data lines 262, 266 and 269 at V_(BL) _(_)_(high) is lowered to the source voltage V_(PL) at a time t4 to end theerase. One or more of the resistance variable memory cells 201, 211 and221 is erased to the second value during the pulse on the access line252 between the times t3 and t4. The resistance variable memory cells201, 211 and 221 that were erased to the second value between the timest3 and t4 may be the same or different than the resistance variablememory cells 201, 211 and 221 programmed to the first value between thetimes t1 and t2.

Specific values of the voltages shown in the timing diagram 300resistance variable memory cell 100 are listed in TABLE I according tovarious embodiments of the invention:

TABLE I SIGNAL VOLTS V_(PL) 1.5 V_(BL) _(—) _(low) 0 V_(BL) _(—) _(high)3 V_(WL) _(—) _(low) 0 V_(WL) _(—) _(highA) 4.5 V_(WL) _(—) _(highB) 6

The voltages listed in TABLE I show that the source 140 is atapproximately 1.5 volts through the acts of programming and erasing.With respect to FIG. 1, the gate terminal 150 is at approximately 4.5volts and the data line 120 is at approximately 0 volts when theresistance variable element 110 is being programmed between the times t1and t2 to store the first value. Current flows from the source 140 tothe data line 120, and the terminal 160 is the source such that agate-source voltage difference V_(GS) is approximately 4.5 volts for theaccess device 130. The gate terminal 150 is at approximately 6 volts andthe data line 120 is at approximately 3 volts when the resistancevariable element 110 is being erased between the times t3 and t4 tostore the second value. Current flows from the data line 120 to thesource 140, and the terminal 170 is the source such that the gate-sourcevoltage difference V_(GS) is approximately 4.5 volts for the accessdevice 130. Through the acts of programming and erasing the gate-sourcevoltage difference V_(GS) is not substantially higher than approximately4.5 volts so that the access device 130 is not compromised.

FIG. 4 is a timing diagram 400 for the array 200 of FIG. 2 according tovarious embodiments of the invention where each of the resistancevariable memory cells 201-223 may be similar or identical to theresistance variable memory cell 100 shown in FIG. 1. The timing diagram400 illustrates voltages in the array 200 during programming and erasingfor the resistance variable memory cells 201, 211 and 221 in the firstrow 250. The voltages are represented on a vertical axis 402 and time tis represented on a horizontal axis 404. Data line voltages on the datalines 262, 266 and 269 are illustrated at the bottom of the timingdiagram 400. A control gate voltage on the access line 252 and the gateterminals 150 of the access devices 130 are illustrated above the dataline voltages. Control gate voltages on the access lines 256 and 259 maybe the same as the control gate voltage on the access line 252.

The resistance variable memory cells 201, 211 and 221 are programmedand/or erased according to the timing diagram 400 to store the samevalues that were programmed and/or erased according to the timingdiagram shown in FIG. 3. The voltages on the data lines 262, 266 and 269in timing diagram 400 are similar to the voltages on the data lines 262,266 and 269 in timing diagram 300 and will not be further described forpurposes of brevity and clarity. The difference is that the pulses onthe access line 252 are merged into a single signal from the time t1 tothe time t4. In other words, instead of returning the control gatevoltage to V_(WL) _(_) _(low) between times t2 and t3, the control gatevoltage is simply raised from V_(WL) _(_) _(highA) to V_(WL) _(_)_(highB).

All of the resistance variable memory cells that are being programmedmay be programmed at the same time with a first control gate voltage.All of the resistance variable memory cells that are being erased may beerased at the same time with a second control gate voltage according tovarious embodiments of the invention.

FIG. 5 is an electrical schematic diagram of an apparatus in the form ofa resistance variable memory cell 500 according to various embodimentsof the invention. The resistance variable memory cell 500 includes aresistance variable element 510. A data line 520 is coupled to an accessdevice 530, and the access device 530 is coupled to the resistancevariable element 510. A data line voltage may be provided on the dataline 520 when an operation is performed on the resistance variableelement 510. In contrast to the embodiment of FIG. 1, the resistancevariable element 510 is coupled between the access device 530 and acommon source 540. The access device 530 is a FET and in particular ann-channel FET. The access device 530 includes a gate terminal 550coupled to an access line (not shown), a first terminal 560 coupled tothe data line 520 and a second terminal 570 coupled to the resistancevariable element 510. The access device 530 can be controlled by acontrol gate voltage on the gate terminal 550 and provided on the accessline. The source 540 may be coupled to thousands or millions of otherresistance variable memory cells and can have a common source voltagethat is substantially constant. The access device 530 may allow currentto flow between the data line 520 and the source 540 when it is switchedon by the potential on its gate terminal 550. The first terminal 560 canbe a drain or a source and the second terminal 570 can be a drain or asource depending on the direction of current in the access device 530.The data line 520 may be used to sense a data state of the resistancevariable element 510. The data state of the resistance variable element510 can be read by measuring a resistance value of the resistancevariable element 510 which can include sensing a value of a currentflowing through the resistance variable element 510. Each of theresistance variable memory cells 201-223 in the array 200 shown in FIG.2 may be similar or identical to the resistance variable memory cell 500shown in FIG. 5 and includes the access device 530 coupled to theresistance variable element 510.

The resistance variable memory cell 500 can be programmed or erasedaccording to the timing diagrams 300 and 400 shown in FIGS. 3 and 4although the voltages are different than the voltages shown in Table I.Specific values of the voltages shown in the timing diagrams 300 and 400for the resistance variable memory cell 500 are listed in TABLE IIaccording to various embodiments of the invention:

TABLE II SIGNAL VOLTS V_(PL) 1.5 V_(BL) _(—) _(low) 0 V_(BL) _(—)_(high) 3 V_(WL) _(—) _(low) 0 V_(WL) _(—) _(highA) 4.5 V_(WL) _(—)_(highB) 6.4The voltages listed in TABLE II show that the source 540 is atapproximately 1.5 volts through the acts of programming and erasing.With respect to FIG. 5, the gate terminal 550 is at approximately 4.5volts and the data line 520 is at approximately 0 volts when theresistance variable element 510 is being programmed between the times t1and t2 to store the first value. Current flows from the source 540 tothe data line 520, and the terminal 560 is the source such that agate-source voltage difference V_(GS) is approximately 4.5 volts for theaccess device 530. The gate terminal 550 is at approximately 6.4 voltsand the data line 520 is at approximately 3 volts when the resistancevariable element 510 is being erased between the times t3 and t4 tostore the second value. Assuming a voltage drop of about 0.4V on theresistance variable element 510, the gate to source voltage in this caseis approximately 4.5V. Current flows from the data line 520 to thesource 540, and the terminal 570 is the source such that the gate-sourcevoltage difference V_(GS) is approximately 4.5 volts for the accessdevice 530. Through the acts of programming and erasing the gate-sourcevoltage difference V_(GS) is not substantially higher than approximately4.5 volts so that the access device 530 is not compromised.

A resistance variable memory cell may have an access device that is ap-channel FET. FIG. 6 is an electrical schematic diagram of an apparatusin the form of a resistance variable memory cell 600 according tovarious embodiments of the invention. The resistance variable memorycell 600 includes a resistance variable element 610 coupled between adata line 620 and an access device 630. A data line voltage may beprovided on the data line 620 when an operation is performed on theresistance variable element 610. The access device 630 is coupledbetween the resistance variable element 610 and a common source 640. Theaccess device 630 is a FET and in particular a p-channel FET. The accessdevice 630 includes a gate terminal 650 coupled to an access line (notshown), a first terminal 660 coupled to the resistance variable element610 and a second terminal 670 coupled to the source 640. The accessdevice 630 can be controlled by a control gate voltage on the gateterminal 650 and provided on the access line. The source 640 may becoupled to hundreds or thousands of other resistance variable memorycells and can have a common source voltage that is substantiallyconstant. The access device 630 may allow current to flow between thedata line 620 and the source 640 when it is switched on by the potentialon its gate terminal 650. The first terminal 660 can be a drain or asource and the second terminal 670 can be a drain or a source dependingon the direction of current in the access device 630. The data line 620may be used to sense a data state of the resistance variable element610. The data state of the resistance variable element 610 can be readby measuring a resistance value of the resistance variable element 610which can include sensing a value of a current flowing through theresistance variable element 610. Each of the resistance variable memorycells 201-223 in the array 200 shown in FIG. 2 may be similar oridentical to the resistance variable memory cell 600 shown in FIG. 6 andincludes the access device 630 coupled to the resistance variableelement 610.

FIG. 7 is a timing diagram 700 for the array 200 of FIG. 2 according tovarious embodiments of the invention where each of the resistancevariable memory cells 201-223 may be similar or identical to theresistance variable memory cell 600 shown in FIG. 6. The timing diagram700 illustrates voltages in the array 200 during a programming operationand/or an erasing operation for the resistance variable memory cells201, 211 and 221 in the first row 250. The voltages are represented on avertical axis 702 and time t is represented on a horizontal axis 704.Data line voltages on the data lines 620, 262, 266 and 269 areillustrated at the bottom of the timing diagram 700. A control gatevoltage on the access line 252 and the gate terminals 650 of the accessdevices 630 are illustrated above the data line voltages. Control gatevoltages on the access lines 256 and 259 may be the same as the controlgate voltage on the access line 252.

The control gate voltage on the access line 252 is at V_(WL) _(_)_(high) which can be V_(BL) _(_) _(high) or a supply voltage Vcc beforeprogramming begins. Programming begins at a time t1 when the controlgate voltage on the access line 252 falls to a first pulse at a voltageV_(WL) _(_) _(lowA) which is sufficient to switch on the access devices630 to program the first value into one or more of the resistancevariable memory cells 201-223. One or more of the data lines 262, 266and 269 are held at a standby data line voltage. The standby data linevoltage can be substantially equal to a source voltage V_(PL) (thepotential of the source 640) such that none of the resistance variablememory cells 201-223 coupled to a data line 262, 266 and 269 at thesource voltage V_(PL) is programmed. One or more of the data lines 262,266 and 269 are brought to a lower voltage V_(BL) _(_) _(low) at thetime t1 to program the resistance variable memory cells 201, 211 and 221coupled to the data lines 262, 266 and 269 at V_(BL) _(_) _(low) to thefirst value. The voltage V_(BL) _(_) _(low) is lower than the sourcevoltage V_(PL). The pulse on the access line 252 ends at a time t2 whenthe potential of the access line 252 rises to V_(WL) _(_) _(low). Thepotential of the data lines 262, 266 and 269 at V_(BL) _(_) _(low) israised to the source voltage V_(PL) at the time t2 to end theprogramming. One or more of the resistance variable memory cells 201,211 and 221 is programmed to the first value during the pulse on theaccess line 252 between the times t1 and t2.

Erasing begins at a time t3 when the control gate voltage on the accessline 252 falls from V_(WL) _(_) _(high) to begin a second pulse at avoltage V_(WL) _(_) _(lowB) which is sufficient to switch on the accessdevices 630 to erase the second value into one or more of the resistancevariable memory cells 201-223. The voltage V_(WL) _(_) _(lowB) is higherthan the voltage V_(WL) _(_) _(lowA). A difference between the voltageV_(WL) _(_) _(lowA) and the voltage V_(WL) _(_) _(lowB) is less than orequal to the source voltage V_(PL). The voltage V_(WL) _(_) _(lowB) maybe substantially equal to the voltage V_(WL) _(_) _(lowA) plus thesource voltage V_(PL). One or more of the data lines 262, 266 and 269are held at the source voltage V_(PL) such that none of the resistancevariable memory cells 201-223 coupled to a data line 262, 266 and 269 atthe source voltage V_(PL) is erased. One or more of the data lines 262,266 and 269 are raised to a higher voltage V_(BL) _(_) _(high) at thetime t3 to erase one or more of the resistance variable memory cells201, 211 and 221 coupled to the data lines 262, 266 and 269 at V_(BL)_(_) _(high) to the second value. The voltage V_(BL) _(_) _(high) ishigher than the source voltage VPL. The pulse on the access line 252ends and the potential of the data lines 262, 266 and 269 at V_(BL) _(_)_(high) is lowered to the source voltage V_(PL) at a time t4 to end theerase. One or more of the resistance variable memory cells 201, 211 and221 is erased to the second value during the pulse on the access line252 between the times t3 and t4. The resistance variable memory cells201, 211 and 221 that were erased to the second value between the timest3 and t4 may be the same or different than the resistance variablememory cells 201, 211 and 221 programmed to the first value between thetimes t1 and t2.

Specific values of the voltages shown in the timing diagram 700resistance variable memory cell 600 are listed in TABLE III according tovarious embodiments of the invention:

TABLE III SIGNAL VOLTS V_(PL) 1.5 V_(BL) _(—) _(low) 0 V_(BL) _(—)_(high) 3 V_(WL) _(—) _(high) 3 V_(WL) _(—) _(lowA) −3 V_(WL) _(—)_(lowB) −1.5The voltages listed in TABLE III show that the source 640 is atapproximately 1.5 volts through the acts of programming and erasing.With respect to FIG. 6, the gate terminal 650 is at approximately −3volts and the data line 620 is at approximately 0 volts when theresistance variable element 610 is being programmed between the times t1and t2 to store the first value. Current flows from the source 640 tothe data line 620, and the terminal 670 is the source such that agate-source voltage difference V_(GS) is approximately −4.5 volts forthe access device 630. The gate terminal 650 is at approximately −1.5volts and the data line 120 is at approximately 3 volts when theresistance variable element 610 is being erased between the times t3 andt4 to store the second value. Current flows from the data line 620 tothe source 640, and the terminal 660 is the source such that thegate-source voltage difference V_(GS) is approximately −4.5 volts forthe access device 630. Through the acts of programming and erasing thegate-source voltage difference V_(GS) is not substantially lower thanapproximately −4.5 volts so that the access device 630 is notcompromised.

FIG. 8 is a timing diagram 800 for the array 200 of FIG. 2 according tovarious embodiments of the invention where each of the resistancevariable memory cells 201-223 may be similar or identical to theresistance variable memory cell 600 shown in FIG. 6. The timing diagram800 illustrates voltages in the array 200 during programming and erasingfor the resistance variable memory cells 201, 211 and 221 in the firstrow 250. The voltages are represented on a vertical axis 802 and time tis represented on a horizontal axis 804. Data line voltages on the datalines 262, 266 and 269 are illustrated at the bottom of the timingdiagram 800. A control gate voltage on the access line 252 and the gateterminals 650 of the access devices 630 are illustrated above the dataline voltages. Control gate voltages on the access lines 256 and 259 maybe the same as the control gate voltage on the access line 252.

The resistance variable memory cells 201, 211 and 221 are programmedand/or erased according to the timing diagram 800 to store the samevalues that were programmed and/or erased according to the timingdiagram shown in FIG. 7. The voltages on the data lines 262, 266 and 269in timing diagram 800 are similar to the voltages on the data lines 262,266 and 269 in timing diagram 700 and will not be further described forpurposes of brevity and clarity. The difference is that the pulses onthe access line 252 are merged into a single signal from the time t1 tothe time t4. In other words, instead of returning the control gatevoltage to V_(WL) _(_) _(low) between times t2 and t3, the control gatevoltage is simply raised from V_(WL) _(_) _(lowA) to V_(WL) _(_)_(lowB).

FIG. 9 is an electrical schematic diagram of an apparatus in the form ofa resistance variable memory cell 900 according to various embodimentsof the invention. The resistance variable memory cell 900 includes aresistance variable element 910. A data line 920 is coupled to an accessdevice 930, and the access device 930 is coupled to the resistancevariable element 910. A data line voltage may be provided on the dataline 920 when an operation is performed on the resistance variableelement 910. In contrast to the embodiment of FIG. 1, the resistancevariable element 910 is coupled between the access device 930 and acommon source 940. The access device 930 is a FET and in particular ap-channel FET. The access device 930 includes a gate terminal 950coupled to an access line (not shown), a first terminal 960 coupled tothe data line 920 and a second terminal 970 coupled to the resistancevariable element 910. The access device 930 can be controlled by acontrol gate voltage on the gate terminal 950 and provided on the accessline. The source 940 may be coupled to thousands or millions of otherresistance variable memory cells and can have a common source voltagethat is substantially constant. The access device 930 may allow currentto flow between the data line 920 and the source 940 when it is switchedon by the potential on its gate terminal 950. The first terminal 960 canbe a drain or a source and the second terminal 970 can be a drain or asource depending on the direction of current in the access device 930.The data line 920 may be used to sense a data state of the resistancevariable element 910. The data state of the resistance variable element910 can be read by measuring a resistance value of the resistancevariable element 910 which can include sensing a value of a currentflowing through the resistance variable element 910. Each of theresistance variable memory cells 201-223 in the array 200 shown in FIG.2 may be similar or identical to the resistance variable memory cell 900shown in FIG. 9 and includes the access device 930 coupled to theresistance variable element 910.

The resistance variable memory cell 900 can be programmed or erasedaccording to the timing diagrams 700 and 800 shown in FIGS. 7 and 8although the voltages are different than the voltages shown in TableIII. Specific values of the voltages shown in the timing diagrams 700and 800 for the resistance variable memory cell 900 are listed in TABLEIV according to various embodiments of the invention:

TABLE IV SIGNAL VOLTS V_(PL) 1.5 V_(BL) _(—) _(low) 0 V_(BL) _(—)_(high) 3 V_(WL) _(—) _(high) 3 V_(WL) _(—) _(lowA) −3.4 V_(WL) _(—)_(lowB) −1.5

The voltages listed in TABLE IV show that the source 940 is atapproximately 1.5 volts through the acts of programming and erasing.With respect to FIG. 9, the gate terminal 950 is at approximately −3.4volts and the data line 920 is at approximately 0 volts when theresistance variable element 910 is being programmed between the times t1and t2 to store the first value. Current flows from the source 940 tothe data line 920, and the terminal 970 is the source such that agate-source voltage difference V_(GS) is approximately −4.5 volts forthe access device 930. The gate terminal 950 is at approximately −1.5volts and the data line 920 is at approximately 3 volts when theresistance variable element 910 is being erased between the times t3 andt4 to store the second value. Current flows from the data line 920 tothe source 940, and the terminal 960 is the source such that thegate-source voltage difference V_(GS) is approximately −4.5 volts forthe access device 930. Through the acts of programming and erasing thegate-source voltage difference V_(GS) is not substantially lower thanapproximately −4.5 volts so that the access device 930 is notcompromised.

FIG. 10 is a flow diagram of a method 1000 according to variousembodiments of the invention. In block 1010, the method 1000 starts. Inblock 1020, a first access device is switched on with a first controlgate voltage and a first data line voltage is provided to a first dataline. A first resistance variable element coupled to the first accessdevice is then programmed in a first operation. In block 1030, a seconddata line voltage is provided to a second data line that is differentthan the first data line voltage. A second access device is switched onwith a second control gate voltage that is different than the firstcontrol gate voltage. A second resistance variable element coupled tothe second access device is then erased in a second operation. In block1040, the method 1000 ends. Various embodiments may have more or feweractivities than those shown in FIG. 10. In some embodiments, theactivities may be repeated, and/or performed in serial or parallelfashion. Some embodiments may comprise the same activities in adifferent order.

FIG. 11 is a block diagram of an apparatus in the form of a memorydevice 1100 according to various embodiments of the invention. Thememory device 1100 can include a plurality of memory cells 1101 in amemory array 1102. The memory cells 1101 can be arranged in rows andcolumns along with access lines 1104 and first data lines 1106. Thememory device 1100 can use the access lines 1104 and the first datalines 1106 to transfer data to and from the memory cells 1101. A rowdecoder 1107 and a column decoder 1108 can decode address signals A0through AX on address lines 1109 to determine which ones of the memorycells 1101 are to be accessed.

A sense amplifier circuit 1110 can operate to determine the value ofdata read from memory cells 1101 and the data read is communicated inthe form of signals to the first data lines 1106. The sense amplifiercircuit 1110 can also use the signals on the first data lines 1106 todetermine values of data to be written to the memory cells 1101.

The memory device 1100 can include circuitry 1111 to transfer databetween the memory array 1102 and input/output (I/O) lines 1112. SignalsDQ0 through DQN on the I/O lines 1112 can represent data read from orwritten into the memory cells 1101. The I/O lines 1112 can include nodeswithin the memory device 1100 (or alternatively, pins, solder balls, orother interconnect technologies such as controlled collapse chipconnection (C4), or flip chip attach (FCA)) on a package where thememory device 1100 can reside. Other devices external to memory device1100 can communicate with the memory device 1100 through the I/O lines1112, the address lines 1109, or control lines 1120. For example, suchexternal devices can include a memory controller or a processor.

The memory device 1100 can perform memory operations, such as a readoperation, to read data from selected ones of the memory cells 1101, anda write operation to store data into selected ones of the memory cells1101. A memory control unit 1122 controls memory operations based onsignals on the control lines 1120. Examples of the signals on thecontrol lines 1120 can include one or more clock signals and othersignals to indicate which operation (e.g., a write or a read operation)the memory device 1100 can or should perform. Other devices external tothe memory device 1100 can control the values of the control signals onthe control lines 1120. The external devices can include, for example, aprocessor or a memory controller. Specific values of a combination ofthe control signals on the control lines 1120 can produce a command,such as a write or read command for example, that can cause the memorydevice 1100 to perform a corresponding memory operation. Thecorresponding memory operation can include, for example, a write or aread operation.

Each of the memory cells 1101 can be programmed or erased to store datarepresenting a value of a single bit or a value of multiple bits such astwo, three, four, or a higher number of bits. For example, each of thememory cells 1101 can be programmed or erased to store data representinga binary value “0” or “1” of a single bit. The single bit per cell issometimes called a single level cell. In another example, each of thememory cells 1101 can be programmed or erased to store data representinga value representing multiple bits, such as one of four possible values“00,” “01,” “10,” and “11” of two bits, one of eight possible values“000,” “001,” “010,” “011,” “100,” “101,” “110,” and “111” of threebits, or one of another set of values of multiple bits. A cell that hasan ability to store multiple bits is sometimes referred to as amulti-level cell or multi-state cell.

The memory device 1100 can receive a supply voltage, including supplyvoltage signals Vcc and Vss, on a first supply line 1130 and a secondsupply line 1132, respectively. The supply voltage signal Vss canoperate at a ground potential. The ground potential can have a value ofapproximately zero volts. The supply voltage signal Vcc can include anexternal voltage supplied to the memory device 1100 from an externalpower source such as a battery or an alternating current to directcurrent (AC-DC) converter circuitry.

The circuitry 1111 of memory device 1100 can include a select circuit1124 and an input/output (I/O) circuit 1126. Select circuit 1124 canrespond to signals SEL1 through SELn to select signals on first datalines 1106 and second data lines 1113 that can represent the data readfrom or to be written into memory cells 1101. Column decoder 1108 canselectively activate the SEL1 through SELn signals based on the A0through AX address signals on address lines 1109. Select circuit 1124can select the signals on first data lines 1106 and second data lines1113 to provide communication between memory array 1102 and I/O circuit1126 during read and write operations.

The memory cells 1101 can comprise one or more of the resistancevariable memory cells 100, 500, 600 and 900 shown in FIGS. 1, 5, 6 and9, respectively. The memory device 1100 can include the array 200 ofresistance variable memory cells shown in FIG. 2 including one or moreof the resistance variable memory cells 100, 500, 600 and 900 shown inFIGS. 1, 5, 6 and 9, respectively.

The methods described herein can result in higher drive current from anaccess device in a resistance variable memory cell. This can lead to asignificant performance improvement over conventional technology.

Example structures and methods of resistance variable elements have beendescribed. Although specific embodiments have been described, it will beevident that various modifications and changes may be made to theseembodiments. Accordingly, the specification and drawings are to beregarded in an illustrative rather than a restrictive sense.

The Abstract of the Disclosure is provided to comply with 37 C.F.R.§1.72(b), requiring an abstract that allows the reader to quicklyascertain the nature of the technical disclosure. It is submitted withthe understanding that it will not be used to interpret or limit theclaims. In addition, in the foregoing Detailed Description, it may beseen that various features are grouped together in a single embodimentfor the purpose of streamlining the disclosure. This method ofdisclosure is not to be interpreted as limiting the claims. Thus, thefollowing claims are hereby incorporated into the Detailed Description,with each claim standing on its own as a separate embodiment.

What is claimed is:
 1. A method comprising: performing a first operation on a first resistance variable element coupled to a first access device, wherein performing the first operation comprises providing the first access device with a first control gate voltage, the first resistance variable element and the first access device being coupled between a first data line at a first data line voltage and a common source at a common source voltage; and performing a second operation on a second resistance variable element coupled to a second access device, wherein performing the second operation comprises providing the second access device with a second control gate voltage that is different than the first control gate voltage, the second resistance variable element and the second access device being coupled between a second data line at a second data line voltage that is different than the first data line voltage and the common source at the common source voltage. 